The invention relates to on a circuit arrangement for monitoring the air volume in a vehicle tire and comprising pressure and temperature rotating sensors fastened at a vehicle wheel, and a transmitter for transmitting sensed values to an evaluating circuit. In order to monitor the air volume in the tire of a motor vehicle in a known circuit arrangement of this type, according to WO 87/041 23, the temperature and pressure of the air in the tire is sensed by semiconductor sensors and corresponding measurement values are transmitted cyclically via a multiplexing control from the rotating wheel via a converter to an evaluating circuit which is fixed with respect to the vehicle. The air volume with which the tire is filled, is determined from the ratio of tire pressure and tire air temperature (PT) and is compared with an allowable limiting value. As soon as the air volume in one of the vehicle tires reaches or falls below the predetermined limiting value, an optical or acoustic signal is issued, and the driver of the vehicle is accordingly alerted to the risk of overstressing the tire.
In order to monitor the air volume in the vehicle tire, it is necessary that the pressure and the temperature of the air in the tire be known as exactly as possible. However, since the air in the tire and the wheel rim can have different temperatures when driving and, since the temperature sensor is inserted in the wheel rim and can therefore be thermally uncoupled from the wheel rim only incompletely, the air temperature in the tire can not be measured with the required accuracy. There is always a temperature difference between the tire air and the measurement value of the temperature sensor.